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开发稳定高效的可见光吸收的氧化物半导体光催化剂是太阳能光催化分解水的一个重要研究方向.最近我们提出(J.Mater.Chem.A,2020,8,6863?6873),具有室温铁电性质的BiFeO3(BFO)薄膜体系表现出低光电流密度响应是由于铁电畴壁/界面处的电荷复合,而该作用在纳米粒子催化剂体系中应该会大大减少.为了证明这一观点,我们通过溶胶-凝胶法合成了BFO纳米粒子,并进行了Mn掺杂获得了Mn-BFO.光催化水氧化反应表明,纯BFO具有光催化氧化水的活性,析氧数率达到70μmol h-1 g-1;而Mn掺杂量优化(0.05％)后的Mn-BFO在可见光(λ ≥420 nm)照射下的析氧活性大大提高,达到255μmol h-1 g-1.带隙研究表明,通过改变Mn的掺杂量,可以将Mn-BFO的带隙从2.1 eV调整为1.36 eV.DFT计算表明,表面的Fe物种是水氧化的活性位点,而不是Mn物种,因为Mn掺杂后Fe物种的水氧化过电势0.51 V,是所考察的表面Fe和Mn物种中过电势中最低的.因此,Mn-BFO光催化水氧化活性的增强可归因于半导体带隙变窄后吸收更多的可见光、降低了的水氧化过电势以及抑制光生电荷复合这几项的协同效应.这项工作表明,锰掺杂是提高纳米粒子铁电BFO光催化剂固有光催化水氧化活性的有效策略.本文采用溶胶-凝胶法成功制备了锰掺杂的BFO样品,并使用XRD,DRS,Mott-Schottky,XPS和PL等进行了表征.XRD分析结果表明,Mn掺杂后,BFO的(110)和(104)衍射峰向高位衍射角方向位移合并产生一个更宽的峰,表明Mn的掺杂引起BFO晶格结构变形.DRS光谱分析表明,Mn的掺杂可以拓展可见光的吸收,从纯BFO的550 nm吸收边(对应于2.1 eV的带隙)扩展到BFO-2的800 nm(对应于1.46 eV的带隙)吸收带边.这些结果与用DFT计算DOS分析得到的BFO和BFO-2理论带隙值2.05和1.53 eV一致.Mott-Schottky分析表明,BFO和BFO-2是p型半导体,其平带(Vfb)电势分别为1.7和1.6 V vs NHE,VB位置估计分别为2.0和1.9 V vs NHE,而CB位置估计分别为-0.11和0.44 V vs NHE.因此,Mn-BFO在热力学有利于光催化OER但不利于HER.从Mn-BFO的XPS光谱可以看出除了Bi,Fe和O光谱外,也可以在641.20和652.7 eV处观察到出Mn 2p3/2和2p1/2,表明Mn是以Mn3+的形式均匀地掺入BFO的晶格中.对一系列不同含量Mn掺杂的Mn-BFO的光催化OER活性表明研究表明,0.05％Mn掺杂的BFO-2的光催化OER活性最优,其析氧活性达到255μmol h-1 g-1,这是迄今为止未加载任何助催化剂的BFO的最高固有光催化OER活性值.PL光谱(290 nm激发)显示,与纯BFO相比,BFO-2的荧光强度弱得多,表明Mn的掺杂可以抑制光生电荷的复合.DFT计算显示,BFO的表面Fe活性中心的OER过电势为0.93 V;而对于Mn掺杂的BFO-2,理论计算得到表面Fe中心和Mn中心的析氧过电位分别为0.51和0.60 V.由此可见,Mn掺杂不改变BFO的析氧活性中心,但是可大大降低Fe活性中心OER过电位,这与锰掺杂的BFO-2表现出比BFO更高光催化氧化水的催化活性实验结果相一致.综上所述,在纳米粒子光催化体系中,Mn掺杂的BFO可以促进可见光的吸收,促进光生电荷有效分离,降低表面Fe基活性中心氧化水的过电位,从而显著提高光催化氧化水的活性.Mn的掺杂对于铁电性质的影响及其光催化活性的关系,有待进一步探索.“,”The development of stable and efficient visible light-absorbing oxide-based semiconductor photo-catalysts is a desirable task for solar water splitting applications. Recently, we proposed that the low photocurrent density in film-based BiFeO3 (BFO) is due to charge recombination at the interface of the domain walls, which could be largely reduced in particulate photocatalyst systems. To demon-strate this hypothesis, in this work we synthesized particulate BFO and Mn-doped BiFeO3 (Mn-BFO) by the sol-gel method. Photocatalytic water oxidation tests showed that pure BFO had an intrinsic photocatalytic oxygen evolution reaction (OER) activity of 70 μmol h-1 g-1, while BFO-2, with an optimum amount of Mn doping (0.05％), showed an OER activity of 255 μmol h-1 g-1 under visible light (λ≥ 420 nm) irradiation. The bandgap of Mn-doped BFO could be reduced from 2.1 to 1.36 eV by varying the amount of Mn doping. Density functional theory (DFT) calculations suggested that surface Fe (rather than Mn) species serve as the active sites for water oxidation, because the over-potential for water oxidation on Fe species after Mn doping is 0.51 V, which is the lowest value measured for the different Fe and Mn species examined in this study. The improved photocatalytic water oxidation activity of Mn-BFO is ascribed to the synergistic effect of the bandgap narrowing, which increases the absorption of visible light, reduces the activation energy of water oxidation, and inhibits the recombination of photogenerated charges. This work demonstrates that Mn doping is an effective strategy to enhance the intrinsic photocatalytic water oxidation activity of particulate ferroelectric BFO photocatalysts.